The epidemiologists examined
links between particle pollution and mortality within more than 260 Los
Angeles neighborhoods. (Image courtesy of U.S. Environmental Protection
LOS ANGELES (Sept. 20)-Experts may be significantly underestimating air pollution's
role in causing early death, according to a team of American and Canadian researchers,
who studied two decades' worth of data on residents of the Los Angeles metro area.
When the epidemiologists examined links between particle pollution and mortality
within more than 260 Los Angeles neighborhoods, they found that pollution's
chronic health effects are two to three times greater than earlier believed.
The study appears in the November issue of Epidemiology but was published early
on the journal's Web site.
Among participants, for each increase of 10 micrograms per cubic meter (µg/m3)
of fine particles in the neighborhood's air, the risk of death from any cause
rose by 11 to 17 percent, according to Michael Jerrett, Ph.D., associate professor
of preventive medicine at the Keck School of Medicine of the University of Southern
California and the paper's lead author. Fine particle levels can differ by about
20 µg/m3 from the cleanest parts of Los Angeles to the most polluted.
"By looking at the effects of pollution within communities, not only did
we observe pollution's influence on overall mortality, but we saw specific links
between particulate matter and death from ischemic heart disease, such as heart
attack, as well as lung cancers," Jerrett says. Ischemic heart disease
mortality risks rose by 25 to 39 percent for the 10 µg/m3increase in air
Earlier studies took one or two pollution measures from several cities and
compared health effects among cities. This study digs more deeply, taking pollution
measures at 23 sites within Los Angeles to more accurately reflect air pollution
exposure where residents live and work.
Researchers examined data from 22,906 residents of Los Angeles, Riverside,
San Bernardino and Ventura counties in the American Cancer Society's Cancer
Prevention Study II since 1982. They determined air pollution exposure in 267
different zip codes where participants lived. The vast number of participants
allowed scientists to control for dozens of factors that influence health outcome,
such as smoking, diet and education. Finally, they compiled causes of death
for the 5,856 participants who died by 2000.
When considering air pollution, the epidemiologists specifically looked at
levels of particulate matter, a mixture of airborne microscopic solids and liquid
droplets. That includes acids (such as nitrates), organic chemicals, metals,
dust and allergens.
Small particles less than 2.5 micrometers in diameter pose the greatest problems
to health because they can penetrate deep into the lungs and sometimes even
enter the bloodstream. In this study, the researchers tracked this particulate
matter, called PM2.5 for short, across the neighborhoods of Los Angeles. It
is often found in smoke, vehicle exhaust, industrial emissions and haze, driven
by the burning of fossil fuels. Scientists also tracked ozone pollution, but
found no link between ozone levels and mortality.
Increased deaths from heart disease jibe with the scientists' earlier research
showing links between air pollution and atherosclerosis, a thickening of artery
walls that may lead to heart attack and stroke. They believe particulate matter
may promote inflammatory processes, including atherosclerosis, in key tissues.
"We have convincing evidence that those causes of death that we might expect
from inflammation, ischemic heart disease and lung disorders, are elevated in
areas of higher pollution levels," he says.
Researchers also saw more than a twofold increased risk of death from diabetes,
although numbers of diabetes-related deaths were smaller than those from heart
disease, making findings less reliable. "People who are diabetic may be
more susceptible to day-to-day fluctuations in air pollution," Jerrett
says. "They may experience a state of greater inflammation-related to insulin
resistance-that makes their lungs more receptive to receiving harmful particles."
Jerrett notes that findings might have been affected by participants who moved
during the study or who changed their lifestyle since 1982. Another limitation
is that scientists could only use participants' zip codes, rather than their
home addresses, to determine their home neighborhood.
Researchers will conduct a similar study in New York City to try to duplicate
findings. They hope to determine whether Los Angeles' tailpipe-emission-driven
pollution poses a greater danger than that in the eastern United States, where
power plants and factories contribute more heavily to pollution. They also plan
to better understand pollution's effects on diabetes, and will use more specific
measures to assess pollution within neighborhoods.
Because of the large number of participants in the American Cancer Society's
study (more than a million people in 150 cities), policymakers in the past have
relied heavily on findings from the study to set the nation's air-quality standards.
"These findings should give us some pause to think about what we need
to do as a society," Jerrett says. "Restrictions on tailpipe emissions
have gotten tighter, but there are more trucks and cars on the roads and people
are driving farther. This study may cause us to reflect on how we use our cars,
what cars we drive and whether we can do anything to make tailpipe emissions
from all vehicles less harmful to health."